The present invention relates generally to couplings and methods for imparting simultaneous rotary and longitudinal oscillations to a work piece, for example, a distal element associated operatively with a surgical instrument. In preferred forms, the present invention is embodied in couplings and methods for surgical instruments (e.g., ophthalmic microsurgical instruments) so as to achieve relatively high frequency simultaneous rotary (angular) and longitudinal (linear) oscillations relative to the elongate axis of the surgical instrument""s work piece.
During ophthalmic microsurgery, such as lens removal, instruments are used with either horizontal or axial oscillatory movements. Conventional horizontal or axial oscillatory instruments using piezoelectric technology tend to create heat during surgical procedures which might cause indirect damage to adjacent ocular tissues.
Recently, U.S. Pat. No. 5,609,602 to Machemer et al (the entire content of which is expressly incorporated hereinto by reference) disclosed a relatively high frequency rotary oscillatory coupling which includes a pair of opposed hubs which are independently rotatable about a common axis. Pairs of permanent magnets are provided in the opposed faces of the hubs. Thus, when the proximal hub is continuously rotated in a selected rotational direction by a suitable drive motor, the distal hub will be caused to rotate in that same rotational direction. The distal hub, however, is prevented from rotating a complete rotary cycle and instead reverses its rotary direction with the assistance of a spring member 30. Thus, the continual reversal of the rotary direction of the distal hub will cause oscillatory rotary movement to be imparted to a distal element (e.g., associated operatively with a surgical instrument).
U.S. Pat. No. 5,717,266 to Maynard, Jr. (the entire content of which is expressly incorporated hereinto by reference) discloses an oscillatory drive having a driven rotor that is mounted on a shaft and includes plural driven permanent magnets disposed thereon. A spring arrangement is coupled to the driven rotor and limits both clockwise and counterclockwise rotation. First and second driving rotors are mounted on the shaft on one and another sides of the driven rotor. The drive mechanism is such that spring-limited oscillatory rotary movements reciprocally in the clockwise and counterclockwise directions are imparted to the driven rotor. The structures of the Maynard, Jr. ""266 patent, however, appear incapable of imparting both rotary and longitudinal oscillations to the driven rotor.
There are a number of prior proposals for imparting simultaneous torsional and longitudinal oscillations to a medical handpiece tip, as shown in U.S. Pat. No. 4,504,264 to Kelman, U.S. Pat. No. 5,911,699 to Anis et al, U.S. Pat. No. 5,722,945 to Anis et al and U.S. Pat. No. 6,077,285 to Boukhny (the entire content of each patent being expressly incorporated hereinto by reference). IN this regard, the Kelman ""264 patent discloses a hand-held surgical instrument having a working tip which, in addition to longitudinal high frequency vibration, is also capable of comparatively low frequency lateral oscillations. The Anis et al ""699 and Anis et al ""945 patents each disclose a medical handpiece having a fragmenting surface formed at a working tip which is simultaneously rotated and reciprocated ultrasonically so that tissue is fragmented. The Boukhny ""285 patent discloses a medial handpiece having two sets of piezoelectric elements which are polarized to produce longitudinal and torsional motion.
Broadly, in one aspect, the present invention is embodied in magnetic couplings which simultaneously impart reciprocal rotary and longitudinal motions or oscillations to a work element. In preferred embodiments, the magnetic couplings of the present invention are comprised of a drive shaft, an output shaft coaxially aligned with the drive shaft relative to a central axis, and drive and driven magnet assemblies connected operatively to the drive and output shafts, respectively. The drive and driven magnet assemblies include permanent magnets arranged to translate continuous rotation of the drive shaft into simultaneous rotary and longitudinal movements of the driven magnet assembly relative to the drive axis. In this regard, the drive magnet assembly most preferably includes at least one pair of permanent magnets circumferentially spaced-apart and longitudinally staggered relative to one another. This circumferential and longitudinal separation thus cooperatively effects the movement of the permanent magnets of the driven magnet assembly to cause movements in both the circumferential and longitudinal directions. Thus, the arrangement of the permanent magnets of the drive magnet assembly is such to create a magnetic xe2x80x9ccamxe2x80x9d of sorts which affects the movements of the driven magnet assembly.
Most preferably, a resilient support member exhibiting torsional and longitudinal resiliency (e.g., an annular elastomeric disc) is operatively connected to the output shaft to allow for such simultaneous rotary and longitudinal movements thereof. In addition, the resilient support member establishes limits on the extent of rotary and longitudinal movements of the driven magnet assembly thereby allowing for simultaneous reciprocal oscillations in both rotational and longitudinal directions.
Surgical instruments of the present invention which employ such magnetic couplings will typically include a distal work element which connected to the driven magnet assembly so as to be capable of reciprocal simultaneous movements in both rotational and longitudinal directions relative to the work element""s central axis. Most preferably, therefore, the surgical instrument is hand-held and will include a drive motor which is connected operatively to a drive shaft so as to impart continuous rotational motion to the drive magnet assembly.
It would also be highly desirable, particularly in the field of surgical instruments, if a power supply could be provided to minimize any net torque and/or vibration on a drive assembly and hence the instrument itself (e.g., so as to minimize (if not eliminate entirely) noticeable movements of the surgical instrument that might adversely affect the attending surgeon""s manipulation of the instrument). According to another aspect of the present invention, a power supply which addresses such a need is also provided.
In this regard, the preferred power supply in accordance with the present invention minimizes any net torque and/or vibration produced on a drive assembly. In especially preferred embodiments, the power supply of the present invention comprises a control circuit which controls the angular velocity of a drive assembly (e.g., the motor and drive magnet assembly) so that its angular velocity is maintained at a constant level. Preferably, the control circuit is capable of quickly adjusting the angular velocity of the drive assembly back to the constant level if the rotational speed of drive assembly were to deviate therefrom because of, for example, a force load imposed on the drive assembly. Most preferably, this adjustment is accomplished in less time as compared to the time required for one rotation of the drive assembly to thus minimize any net torque and/or vibration thereon.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.